The technique of section freeze-dry autoradiography devised in this laboratory will be used to evaluate the relationship of cellular accumulation of organic acids to transepithelial transport in the proximal tubule of the mammalian kidney. Studies of the effect of acetate on the uptake of tritiated p-aminohippuric acid (PAH-H3) in rat renal cortical slices will be continued to determine the mechanism of acetate stimulation of PAH transport. The effects of transport inhibitors on the distribution of PAH-H3 will be further evaluated using ouabain, amiloride, and phlorizin. The effect of arginine on the intrarenal distribution of lysine will be examined in vivo. Efforts will be continued to develop a technique for quantitation of the autoradiographs. The direction of entry of labeled compounds into tubular cells during microperfusion in vivo will be determined by autoradiography.